Method for rapidly judging iron-phosphorus ratio of iron phosphate according to moisture of dihydrate filter cake and application

Abstract

The invention discloses a method for rapidly judging the iron-phosphorus ratio of iron phosphate according to the moisture of a dihydrate filter cake and application, the judgment value of the iron-phosphorus ratio of iron phosphate is obtained through the following formula: Fe / P =-0.6294 * a * moisture + (0.9359 + b), and a and b are process influence coefficients; in the formula,-0.6294 and 0.9359 are constant terms; the moisture content refers to the moisture content of the dihydrate filter cake. According to the method, the quantitative relation between the water content and the iron-phosphorus ratio of the dihydrate filter cake is established through experimental data, the iron-phosphorus ratio of iron phosphate is calculated by utilizing a formula after linear fitting, the problems of long detection time and high cost of a traditional method are solved, and the method has universality for different iron phosphate production processes and is suitable for ammonium-process, sodium-process and iron-process iron phosphate preparation processes.

Description

Technical Field

[0001] The invention relates to the technical field of batteries and relates to a method for quickly judging the iron-phosphorus ratio of iron phosphate according to the moisture content of a dihydrate filter cake and an application thereof. Background Art

[0002] Lithium iron phosphate is a widely used cathode material with high theoretical capacity, low cost and good safety performance. At present, lithium iron phosphate is mostly prepared with iron phosphate as raw material, and its performance is seriously dependent on the quality of iron phosphate. High-purity iron phosphate is the prerequisite for the preparation of high-performance lithium iron phosphate. Too low Fe / P ratio of iron phosphate may lead to unreacted phosphoric acid residue, affecting the efficiency of subsequent lithiation reaction. However, the iron phosphate process cycle is long, and the inherent detection method has a long detection time, high cost, and great influence of human operation. It is not very practical in the production process. Therefore, it is very important to develop a method to quickly determine the iron-phosphorus ratio of iron phosphate. Rapid determination of Fe / P can avoid the production of unqualified intermediates and reduce rework costs. In the continuous production process, it can also avoid equipment malfunction and fluctuations in finished product quality, maintain stable operation of the production line, and improve production efficiency and product consistency.

[0003] Existing technologies have the disadvantages of high requirements for sample uniformity, high cost, susceptibility to interference from other ions, and slow speed. Most of them are more suitable for laboratory research and are not suitable for production lines.

[0004] For example, the patent "A method for determining the phosphorus content in iron phosphate raw materials by weight method, CN117554154A" has a long sample processing time and requires high operator experience, which is suitable for laboratory scenarios with strict precision requirements; the patent "A method for high-precision detection of phosphorus and iron content in iron phosphate, CN103528973A" is susceptible to interference from other ions and requires the additional use of masking agents. The detection cost is high and it is suitable for medium and low precision scenarios; the patent "A method for determining the iron and phosphorus content in iron phosphate for batteries, CN116879332A" has high requirements for sample uniformity and high equipment costs. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for quickly determining the iron-phosphorus ratio of iron phosphate based on the moisture content of the dihydrate filter cake, which can solve the problems of the prior art such as long determination cycle, high cost and unsuitability for production lines.

[0006] The technical solutions of the present invention are as follows: A method for quickly determining the iron-phosphorus ratio of iron phosphate based on the moisture content of the dihydrate filter cake. The iron-phosphorus ratio of iron phosphate is determined by the following formula: Fe / P=-0.6294×a×water+(0.9359+b) Among them, a and b are process influence coefficients, such as stirring frequency, reaction temperature, reaction pH, etc.

[0007] In the formula, -0.6294 and 0.9359 are constant terms; Moisture content refers to the moisture content of the dihydrate filter cake.

[0008] Furthermore, the values of a and b are determined as follows: (1): Under the same process parameters of the ferric phosphate preparation method, the water content and iron-phosphorus ratio of the dihydrate filter cake were tested and recorded multiple times. The iron-phosphorus ratio test method was in accordance with the national standard (GB / T 33822-2017); (2): Change the dosage of one of the process parameters in step (1), repeat the experiment, take the dihydrate filter cake to test the moisture content and iron-phosphorus ratio and record them; (3): Change the amount of another process parameter in step (1), repeat the experiment, take the dihydrate filter cake to test the moisture content and iron-phosphorus ratio and record them; (4): In Excel, the moisture content under different process parameters is used as the variable x, and the iron-phosphorus ratio result is used as the result y. The recorded experimental results are entered and a scatter plot is drawn to analyze the results. The corresponding relationship between y and x is fitted according to the scatter plot to obtain a fitting curve, thereby determining the values of a and b; a=absolute value of the slope of the fitting curve / 0.6294; b = fitting constant term -0.9359; Furthermore, the method for preparing ferric phosphate in step (1) is an ammonium method for preparing ferric phosphate, comprising the following steps: S1: Prepare 40 L of 1.0 mol / L ferrous sulfate solution and 40 L of 1.0 mol / L ammonium dihydrogen phosphate solution; S2: Start stirring the reactor at 400 rpm, and add ferrous sulfate solution and ammonium dihydrogen phosphate solution into the reactor at the same time, and the feeding time is 30 minutes; S3: 2.7 L of 27.5% hydrogen peroxide and 3.4 L of 28% ammonia were added to the reactor simultaneously over a period of 10 min. The pH of the synthesis reaction was controlled at 2.8 and the temperature in the reactor was controlled at 35°C to obtain amorphous iron phosphate. S4: The slurry is washed and filtered using a centrifuge with a washing frequency set to 25 Hz. After washing until the conductivity is less than 5000 μS / cm, the washing water is turned off and the frequency is set to 45 Hz for centrifugal filtration for 20 minutes to obtain filter cake A. S5: Filter cake A, 40 L of pure water, and 0.923 kg of 85% phosphoric acid were added to a reactor and beaten at 600 rpm and 90-98°C for 60 min to obtain ferric phosphate dihydrate slurry; S6: The slurry is washed and filtered using a centrifuge with a washing frequency set to 25 Hz. After washing until the conductivity is less than 1500 μS / cm, the washing water is turned off and the frequency is set to 45 Hz for centrifugal filtration for 20 minutes to obtain a dihydrate filter cake; S7: Take 5 g of the dihydrate filter cake and dry it at 150°C for 10 min. Calculate the moisture content by the mass difference. S8: The dihydrate filter cake obtained in S6 is placed in an oven, dried at 180°C for 4 hours, and then crushed to obtain dihydrated ferric phosphate powder. The dihydrated ferric phosphate powder is placed in a clay box and sent into a muffle furnace, calcined at 580°C for 4 hours, and taken out after the temperature of the muffle furnace drops to room temperature to obtain the ferric phosphate material.

[0009] Furthermore, in step (2): the amount of ammonia water was changed to 4.0 L based on the process parameters of step (1), and the experiment was repeated. The water content and iron-phosphorus ratio of the dihydrate filter cake were tested and recorded.

[0010] Furthermore, in step (3): the amount of phosphoric acid used in the process parameters of step (1) was changed to 1.5 kg, the experiment was repeated, and the water content and iron-phosphorus ratio of the dihydrate filter cake were tested and recorded.

[0011] Furthermore, in step (3): the amount of phosphoric acid used in the process parameters of step (1) was changed to 0.5 kg, the experiment was repeated, and the water content and iron-phosphorus ratio of the dihydrate filter cake were tested and recorded.

[0012] Furthermore, the method for preparing ferric phosphate in step (1) is a sodium method for preparing ferric phosphate.

[0013] Furthermore, the method for preparing ferric phosphate in step (1) is an iron method for preparing ferric phosphate.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) Short time consumption: Conventional Fe / P testing takes 5 to 6 hours, while this method only takes 10 to 20 minutes, which can help the production line quickly determine whether there is any abnormality in the product / process; (2) Simple operation: Conventional Fe / P testing includes steps such as reagent preparation, sample dissolution, and testing. This method only requires calculating the mass difference before and after drying the filter cake; (3) Low cost: The cost of conventional Fe / P testing is 160 yuan per time. The equipment and process involved in this method are the same as those for preparing ferric phosphate, and no other costs are required. On a production line with an annual output of 100,000 tons, the rapid determination of Fe / P based on this method can reduce the number of sample tests by about 20,000, saving about 3 million yuan in testing costs.

[0015] (4) The method provided by the present invention is universally applicable to different ferric phosphate production processes and is suitable for the preparation of ferric phosphate using the ammonium method, sodium method, and iron method.

[0016] (5) The key technical point of the present invention is to establish a quantitative relationship model between the moisture content of the dihydrate filter cake and the iron-phosphorus ratio for the first time, and to use the formula after linear fitting to calculate the iron-phosphorus ratio of iron phosphate, thus solving the problem of long detection time and high cost of traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the fitting curve of moisture content and iron-phosphorus ratio. DETAILED DESCRIPTION

[0018] Example 1 The ammonium process for preparing ferric phosphate comprises the following steps: S1: Prepare 40 L of 1.0 mol / L ferrous sulfate solution and 40 L of 1.0 mol / L ammonium dihydrogen phosphate solution.

[0019] S2: Start stirring the reactor at 400 rpm, and add the ferrous sulfate solution and the ammonium dihydrogen phosphate solution into the reactor at the same time. The feeding time is 30 minutes.

[0020] S3: 2.7 L of 27.5% hydrogen peroxide and 3.4 L of 28% ammonia were added to the reactor simultaneously within 10 min. The pH of the synthesis reaction was controlled at 2.8, and the temperature in the reactor was controlled at 35°C to obtain amorphous iron phosphate.

[0021] S4: The slurry is washed and filtered using a centrifuge. The washing frequency of the centrifuge is set to 25 Hz. After washing until the conductivity is less than 5000 μS / cm, the washing water is turned off and the frequency is set to 45 Hz for centrifugal filtration for 20 minutes to obtain filter cake A.

[0022] S5: Filter cake A, 40 L pure water, and 0.923 kg of 85% phosphoric acid were added to a reactor for slurrying at 600 rpm and kept at 93°C for 60 min to obtain ferric phosphate dihydrate slurry.

[0023] S6: The slurry is washed and filtered using a centrifuge. The washing frequency of the centrifuge is set to 25 Hz. After washing until the conductivity is less than 1500 μS / cm, the washing water is turned off and the frequency is set to 45 Hz for centrifugal filtration for 20 minutes to obtain a dihydrate filter cake.

[0024] S7: Take 5 g of the dihydrate filter cake and dry it at 150°C for 10 min. Calculate the moisture content by the mass difference.

[0025] S8: The dihydrate filter cake obtained in S6 is placed in an oven, dried at 180°C for 4 hours, and then crushed to obtain dihydrated ferric phosphate powder. The dihydrated ferric phosphate powder is placed in a clay box and sent into a muffle furnace, calcined at 580°C for 4 hours, and taken out after the temperature of the muffle furnace drops to room temperature to obtain the ferric phosphate material.

[0026] Example 2 Embodiment 2 of the present invention includes the following steps: All steps are the same as in Example 1. Under the process parameters of Example 1, the water content and iron-phosphorus ratio of the dihydrate filter cake were tested and recorded multiple times. The iron-phosphorus ratio test method refers to the national standard (GB / T 33822-2017); The amount of phosphoric acid used in Example 1 was changed to 0.5 kg, and all other steps were the same as in Example 1. The experiment was repeated five times, and the water content and iron-phosphorus ratio of the dihydrate filter cake were tested and recorded.

[0027] The amount of phosphoric acid used in Example 1 was changed to 1.5 kg. All other steps were the same as in Example 1. The experiment was repeated five times. The water content and iron-phosphorus ratio of the dihydrate filter cake were tested and recorded.

[0028] The amount of ammonia water was changed to 4.2 L based on the process parameters of Example 1. All other steps were the same as in Example 1. The experiment was repeated five times. The water content and iron-phosphorus ratio of the dihydrate filter cake were tested and recorded. The recording results of this embodiment are shown in Table 1.

[0029] Table 1 Experimental results of moisture and iron-phosphorus ratio in Example 2

[0030] In Excel, the moisture content in Table 1 is used as the variable x, and the iron-phosphorus ratio result is used as the result y. The recorded experimental results are entered and a scatter plot is drawn to analyze the results. The corresponding relationship between y and x is fitted according to the scatter plot to obtain the fitting curve as shown below. Figure 1 As shown, the values of a and b are determined; a = absolute value of the slope of the fitting curve / 0.6294 = 0.7805 / 0.6294 = 1.24; b=fitting curve constant term -0.9359=1.438-0.9359=0.5021.

[0031] The iron-phosphorus ratio of the finished ferric phosphate prepared by the ammonium process is determined by the following formula: Fe / P=-0.6294×a×moisture content+(0.9359+b) Where a = 1.24, b = 0.5021. -62.94 and 93.59 in the formula are constant terms, which are values determined after collecting and analyzing a large amount of experimental data in the early stage. This patent directly uses them, and the derivation process will not be repeated here.

[0032] Example 3 The ammonium process for preparing ferric phosphate comprises the following steps: S1-S2 are consistent with those in Example 1 and are not described in detail here; S3: 2.7 L of 27.5% hydrogen peroxide and 3.2 L of 28% ammonia were added to the reactor simultaneously within 10 min. The pH of the synthesis reaction was controlled at 2.6, and the temperature in the reactor was controlled at 35°C to obtain amorphous iron phosphate.

[0033] S4 to S6 are the same as those in Example 1 and are not described in detail here; S7: 5 g of the dihydrate filter cake was dried at 150° C. for 10 min, and the moisture content was calculated by mass difference to be 62.49%. According to a=1.24, b=0.5021 obtained in Example 2 and the formula Fe / P=-62.94×a×moisture+(93.59+b), the iron-to-phosphorus ratio of the iron phosphate was estimated to be 95.03%.

[0034] Example 4 The ammonium process for preparing ferric phosphate comprises the following steps: S1-S2 are consistent with those in Example 1 and are not described in detail here; S3: 2.7 L of 27.5% hydrogen peroxide and 3.6 L of 28% ammonia were added to the reactor simultaneously. The addition was completed within 10 min. The pH of the synthesis reaction was controlled at 3.2, and the temperature in the reactor was controlled at 35°C to obtain amorphous iron phosphate.

[0035] S4 to S6 are the same as those in Example 1 and are not described in detail here; S7: 5 g of the dihydrate filter cake was dried at 150° C. for 10 min, and the moisture content was calculated to be 60.78% by mass difference. According to a=1.24, b=0.5021 obtained in Example 2 and the formula Fe / P=-62.94×a×moisture+(93.59+b), the iron-to-phosphorus ratio of the iron phosphate prepared in this experiment was estimated to be 96.36%.

[0036] Example 5 The ammonium process for preparing ferric phosphate comprises the following steps: S1 to S4 are consistent with those in Example 1 and are not described in detail here; S5: Filter cake A, 40 L pure water, and 2.0 kg of 85% phosphoric acid were added to a reactor for slurrying at 600 rpm and kept at high temperature for 60 min to obtain ferric phosphate dihydrate slurry.

[0037] S6 is consistent with Example 1 and will not be described in detail here; S7: 5 g of the dihydrate filter cake was dried at 150° C. for 10 min, and the moisture content was calculated to be 58.97% by mass difference. According to a=1.24, b=0.5021 obtained in Example 2 and the formula Fe / P=-62.94×a×moisture+(93.59+b), the iron-to-phosphorus ratio of the experimentally prepared iron phosphate was estimated to be 97.78%.

[0038] Comparative Examples of the Present Invention The difference between the comparative example of the present invention and the embodiment is that the operation and method for determining the iron-phosphorus ratio are different, and the following steps are added: placing the dihydrate filter cake in an oven, drying it at 180° C. for 4 hours, and then crushing it to obtain dihydrate iron phosphate powder, charging the dihydrate iron phosphate powder into a clay sagger and sending it into a muffle furnace, calcining it at 580° C. for 4 hours, taking out the iron phosphate after the temperature of the muffle furnace is lowered to room temperature, sampling the iron phosphate to test the Fe content and P content, and calculating the iron-phosphorus ratio according to the formula (Fe / 55.845) / (P / 30.97)*100%, wherein the test method of the Fe content and the P content refers to the national standard (GB / T 33822-2017).

[0039] Comparative Example 1 Comparative Example 1 of the present invention comprises the following steps: S1 to S6 are the same as those in the third embodiment and will not be described again here.

[0040] S7: Place the dihydrate filter cake obtained in S6 into an oven, dry it at 180°C for 4 hours, and then grind it to obtain dihydrated ferric phosphate powder. Place the dihydrated ferric phosphate powder into a clay box and place it into a muffle furnace. Calcined at 580°C for 4 hours, the ferric phosphate powder is taken out after the temperature of the muffle furnace drops to room temperature. S8: The iron phosphate material obtained by treatment S7 was tested for Fe and P content. The Fe content was 36.05%, and the P content was 20.96%. The iron-phosphorus ratio was calculated using the formula (Fe / 55.845) / (P / 30.97)*100%, which was 95.38%.

[0041] Comparative Example 2 Comparative Example 2 of the present invention comprises the following steps: S1 to S6 are the same as those in the fourth embodiment and will not be described again here.

[0042] S7 is the same as comparative example 1, and will not be described again here.

[0043] S8: The iron phosphate material obtained by treatment S7 was tested for Fe and P content. The Fe content was 36.13%, and the P content was 20.86%. The iron-phosphorus ratio was calculated using the formula (Fe / 55.845) / (P / 30.97)*100%, which was 96.05%.

[0044] Comparative Example 3 Comparative Example 3 of the present invention comprises the following steps: S1 to S6 are the same as those in the fifth embodiment and will not be described again here.

[0045] S7 is the same as comparative example 1, and will not be described again here.

[0046] S8: The Fe and P contents of the iron phosphate material obtained by treatment S7 were tested. The Fe content was 36.37%, and the P content was 20.74%. The iron-phosphorus ratio was calculated to be 97.25% using the formula (Fe / 55.845) / (P / 30.97)*100%.

[0047] The iron-phosphorus ratios obtained in Examples 3 to 5 and Comparative Examples 1 to 3 were recorded and analyzed as follows:

[0048] In summary, in the embodiment and the comparative example, when the preparation process of iron phosphate is the same, the iron-phosphorus ratio obtained by the embodiment of the present invention is similar to the iron-phosphorus ratio obtained by the conventional detection method in the daily research and development process, and the deviation rate is less than 1%, indicating that the linear equation fitting of the iron-phosphorus ratio and the water content of the dihydrate filter cake obtained by big data analysis is high, which can be used to estimate the iron-phosphorus ratio of the iron phosphate material. By comparing the experimental duration of the embodiment and the comparative example, it can be concluded that the present invention can quickly judge the iron-phosphorus ratio of iron phosphate.

[0049] The method of the present invention is simple to operate and only requires the use of a rapid moisture detector or an oven and a balance. The Fe / P ratio is related to the degree of crystal development of ferric phosphate dihydrate and is its external manifestation. The degree of crystal structure development directly affects the particle size. The size of the primary particles affects the degree and form of agglomeration, thereby affecting the "water retention rate" of the agglomerates. The more severe the particle agglomeration, the higher the water retention rate and the lower the iron-phosphorus ratio. Therefore, a quantitative relationship between the moisture content of the dihydrate filter cake and the Fe / P ratio can be established through experimental data, and then the iron-phosphorus ratio of the ferric phosphate material after muffle furnace sintering can be estimated by measuring the moisture content of the dihydrate filter cake.

Claims

1. A method for quickly determining the iron-phosphorus ratio of iron phosphate based on the water content of a dihydrate filter cake, characterized in that: The iron-phosphorus ratio of iron phosphate is determined by the following formula: Fe / P=-0.6294×a×water+(0.9359+b) Among them, a and b are process influence coefficients; In the formula, -0.6294 and 0.9359 are constant terms; Moisture content refers to the moisture content of the dihydrate filter cake.

2. The method of claim 1, wherein the method comprises: The values of a and b are as follows: (1) Under the same process parameters for the preparation of ferric phosphate, take the dihydrate filter cake several times to test the moisture content and iron-phosphorus ratio and record them; (2) Change the dosage of one of the process parameters in step (1), repeat the experiment, take the dihydrate filter cake, test the moisture content and iron-phosphorus ratio, and record them; (3) Change the amount of another process parameter in step (1), repeat the experiment, take the dihydrate filter cake to test the moisture content and iron-phosphorus ratio and record them; (4) In Excel, the moisture content under different process parameters is used as the variable x, and the iron-phosphorus ratio result is used as the result y. The recorded experimental results are entered and a scatter plot is drawn to analyze the results. The corresponding relationship between y and x is fitted according to the scatter plot to obtain a fitting curve, thereby determining the values of a and b; a=absolute value of the slope of the fitting curve / 0.6294; b = fitting constant term -0.9359.

3. The method of claim 2, wherein the method comprises: The method for preparing ferric phosphate in step (1) is to prepare ferric phosphate by the ammonium method, which includes the following steps: S1: Prepare 40 L of 1.0 mol / L ferrous sulfate solution and 40 L of 1.0 mol / L ammonium dihydrogen phosphate solution; S2: Start stirring the reactor at 400 rpm, and add ferrous sulfate solution and ammonium dihydrogen phosphate solution into the reactor at the same time, and the feeding time is 30 minutes; S3: 2.7 L of 27.5% hydrogen peroxide and 3.4 L of 28% ammonia were added to the reactor simultaneously over a period of 10 min. The pH of the synthesis reaction was controlled at 2.8 and the temperature in the reactor was controlled at 35°C to obtain amorphous iron phosphate. S4: The slurry is washed and filtered using a centrifuge with a washing frequency set to 25 Hz. After washing until the conductivity is less than 5000 μS / cm, the washing water is turned off and the frequency is set to 45 Hz for centrifugal filtration for 20 minutes to obtain filter cake A. S5: Filter cake A, 40 L pure water, and 0.923 kg of 85% phosphoric acid were added to a reactor and beaten at 600 rpm. The mixture was kept at high temperature for 60 min to obtain ferric phosphate dihydrate slurry. S6: The ferric phosphate dihydrate slurry is washed and filtered using a centrifuge with a washing frequency set to 25 Hz. After washing until the conductivity is less than 1500 μS / cm, the washing water is turned off and the centrifugal filtration is performed at a frequency of 45 Hz for 20 minutes to obtain a dihydrate filter cake. S7: Take 5 g of the dihydrate filter cake and dry it at 150°C for 10 min. Calculate the moisture content by the mass difference. S8: The dihydrate filter cake obtained in S6 is placed in an oven, dried at 180°C for 4 hours, and then crushed to obtain dihydrated ferric phosphate powder. The dihydrated ferric phosphate powder is placed in a clay box and sent into a muffle furnace, calcined at 580°C for 4 hours, and taken out after the temperature of the muffle furnace drops to room temperature to obtain the ferric phosphate material.

4. The method of claim 3, wherein: The high temperature in S5 is 90-98°C.

5. The method of claim 3, wherein: In step (2): change the amount of ammonia water to 4.0 L based on the process parameters of step (1), repeat the experiment, take the dihydrate filter cake, test the moisture content and iron-phosphorus ratio, and record them.

6. The method of claim 4, wherein: In step (3): change the amount of phosphoric acid to 1.5 kg based on the process parameters of step (1), repeat the experiment, take the dihydrate filter cake, test the moisture content and iron-phosphorus ratio, and record them.

7. The method of claim 3, wherein: In step (3): change the amount of phosphoric acid to 0.5 kg based on the process parameters of step (1), repeat the experiment, take the dihydrate filter cake, test the moisture content and iron-phosphorus ratio, and record them.

8. The method of claim 2, wherein the method comprises: The method for preparing ferric phosphate in step (1) is a sodium method for preparing ferric phosphate.

9. The method of claim 2, wherein the method comprises: The method for preparing ferric phosphate in step (1) is to prepare ferric phosphate by the iron method.

10. Application of the method for quickly determining the iron-phosphorus ratio of ferric phosphate based on the water content of the dihydrate filter cake according to claim 2, characterized in that: Used to determine the iron-phosphorus ratio in the iron method, sodium method and ammonium method of preparing ferric phosphate.

Images